|
Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
|
Thread Tools |
30th Sep 2020, 11:42 am | #1 |
Triode
Join Date: Feb 2020
Location: London, UK.
Posts: 21
|
DYNATRON HFC77 schematic / transformer
Hello,
I have a DYNATRON HFC77 radio/turntable with no power at all. I just checked the output from the transformer and there is nothing at all and no resistance on the primary winding. Transformer type 18897 I could replace the transformer but I do not know the output voltages. Does anyone have a schematic? if so could you have a look to see if it says the voltages. there are 4 wires on the output I have included links to photos below. thanks Last edited by AC/HL; 2nd Oct 2020 at 2:52 pm. Reason: Images uploaded |
30th Sep 2020, 12:51 pm | #2 |
Hexode
Join Date: Aug 2007
Location: S.W. London, UK.
Posts: 418
|
Re: DYNATRON HFC77 schematic / transformer
I wouldn't write-off your transformer yet. Looking at your pictures there appears to be a lump under the label. This is probably a thermal fuse which has gone open circuit.
If you're lucky the terminals will be brought out to the TX connector. If not, you can use a scalpel to gently cut away the label until you find the device - usually a small square of plastic with two leads. You have nothing to lose! See post 3 of this thread https://vintage-radio.net/forum/showthread.php?t=154145 Vic Last edited by Vicboduk; 30th Sep 2020 at 1:01 pm. |
30th Sep 2020, 1:04 pm | #3 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
|
Re: DYNATRON HFC77 schematic / transformer
The part circuit I have of the SRX30 show a thermal fuse fitted to the transformer so definitely worth checking.
__________________
Frank |
30th Sep 2020, 1:45 pm | #4 |
Triode
Join Date: Feb 2020
Location: London, UK.
Posts: 21
|
Re: DYNATRON HFC77 schematic / transformer
Thanks a lot for the info,
I removed the paper, The bulges on the sides were just the wires, there does not appear to be a fuse, although I dont know what that type of fuse would look like. how big would the fuse be? would it be embedded deeper somewhere? the other sides are dead flat so no space for much really. thanks Last edited by AC/HL; 2nd Oct 2020 at 2:56 pm. Reason: Images uploaded |
30th Sep 2020, 2:05 pm | #5 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
|
Re: DYNATRON HFC77 schematic / transformer
Where the brown and green wires connect on both sides, lift that black paper, may under there.
The ones I saw in the 70’s were about a cm square a couple of mm thick in translucent plastic and the fuse wires could be seen through the plastic, easy to see if o/c but of course a meter check is best.
__________________
Frank |
30th Sep 2020, 2:25 pm | #6 |
Octode
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,704
|
Re: DYNATRON HFC77 schematic / transformer
I have the Dynatron HFC77 cross referenced to the SRX29 and SA29 Dynatron models. The HFC77 is also listed for the RTS books 1974-75 page 461 and 1975-76 page 483.
Dave |
30th Sep 2020, 2:51 pm | #7 |
Triode
Join Date: Feb 2020
Location: London, UK.
Posts: 21
|
Re: DYNATRON HFC77 schematic / transformer
Thanks to all, Vic, Frank and Dave for the help.
I found the fuse, not under the paper but wedged in a plastic housing under the green and brown wires. I shorted the fuse out and low and behold it fired up. but the transformer quickly got hot and the large capacitor near the bridge rectifier went BANG! it looks like someone could have been in there messing around before me and could have put the mains cable on the wrong connectors. I did photograph all the cables to make sure it went back correctly so not my error. I will keep digging and test the ohm values at the primary and secondaries so I am sure of the primary 240v input. Last edited by AC/HL; 2nd Oct 2020 at 2:58 pm. Reason: Image uploaded |
30th Sep 2020, 2:59 pm | #8 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
|
Re: DYNATRON HFC77 schematic / transformer
Has noted in the link in post #2 there is usually a reason for the fuse blowing, if that large cap went bang it could have been faulty or very likely the rectifier is S//C.
Edit. Yes that’s the type of fuse I remember.
__________________
Frank |
30th Sep 2020, 6:14 pm | #9 |
Octode
Join Date: Sep 2020
Location: Thetford, Norfolk, UK.
Posts: 1,743
|
Re: DYNATRON HFC77 schematic / transformer
The bridge rectifier has almost certainly shorted out. Check/replace that and the cap and fingers crossed you will be good to go. RS sell replacement thermal fuses which would allow you to continue to protect the transformer.
Otherwise I would add a 0.47R fusible resistor in series with the secondary of the transformer to protect against future failures. |
30th Sep 2020, 6:45 pm | #10 |
Triode
Join Date: Feb 2020
Location: London, UK.
Posts: 21
|
Re: DYNATRON HFC77 schematic / transformer
Thanks again all.
I will have another look at the transformer and bridge/cap and post my results. |
1st Oct 2020, 1:25 pm | #11 |
Triode
Join Date: Feb 2020
Location: London, UK.
Posts: 21
|
Re: DYNATRON HFC77 schematic / transformer
It looks like the transformer is "past it" as it immediately gets very hot and is outputting 61 volts and 47 volts so the insulation on the windings must have broken down. "hence the thermal fuse blowing"
Does anyone know where to get a replacement? It's transformer type 18897 According to the schematic it should output 31 volts and 5.8 volts I have not had any luck finding anything similar on google so maybe I will have to use 2 different transformers, one for the 31v and one for the 5.8v. Thanks |
1st Oct 2020, 5:06 pm | #12 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
|
Re: DYNATRON HFC77 schematic / transformer
Does the transformer get hot with the secondaries disconnected, if so it’s is faulty, if not then there is a problem in the rest of the set, possible the rectifier or reservoir caps.
Of course even if it get hot with the secondaries disconnected it is faulty but probably was damaged by a fault in the rest of the set.
__________________
Frank |
1st Oct 2020, 5:57 pm | #13 | |
Triode
Join Date: Feb 2020
Location: London, UK.
Posts: 21
|
Re: DYNATRON HFC77 schematic / transformer
Quote:
once I change the cap and check the bridge ill try it with 2 different transformers, one for the 31v and one for the 5.8v as it will be near impossible to get an exact replacement. |
|
1st Oct 2020, 6:09 pm | #14 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
|
Re: DYNATRON HFC77 schematic / transformer
If the cap popped you still had the secondaries connected.
__________________
Frank |
1st Oct 2020, 6:16 pm | #15 | |
Triode
Join Date: Feb 2020
Location: London, UK.
Posts: 21
|
Re: DYNATRON HFC77 schematic / transformer
Quote:
after disconnecting the secondaries the transformer still gets very hot so im guessing the transformer insulation was breaking down probably the reason the thermal fuse had blown. its a pity I didnt test the transformer and see the high voltage before I plugged in the secondaries. oh well hopefully its just the cap and bridge to be replaced. |
|
1st Oct 2020, 7:17 pm | #16 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,195
|
Re: DYNATRON HFC77 schematic / transformer
Hi If you can post a picture of the transformer we can advise if it would be possible to rewind it
Ed |
1st Oct 2020, 8:26 pm | #17 | |
Triode
Join Date: Feb 2020
Location: London, UK.
Posts: 21
|
Re: DYNATRON HFC77 schematic / transformer
Quote:
https://drive.google.com/file/d/1-rC...WioDu0L36/view https://drive.google.com/file/d/147M...K3_LW4nRr/view https://drive.google.com/file/d/12lt...lw8D6DZQM/view |
|
1st Oct 2020, 9:43 pm | #18 |
Nonode
Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
Posts: 2,874
|
Re: DYNATRON HFC77 schematic / transformer
Hi!
Will this meet your needs? https://www.ebay.co.uk/itm/174260979116 If the 5.8V red and white leads to SKT104 and SKT105 are only used to feed scale lighting lamps, then all you need to do is wire this transformer as follows:– SKT103 yellow goes to tag "0", SKT104 white goes to tag "31.5" SKT105 red goes to tag "26", but add a 1 ohm to 2.2 ohm 2W resistor in series with the red lead to tag "26" to reduce the voltage supplied to the bulbs in order to prolong their life – choose the resistor to give about 5.5V across the bulbs; . . .and connect the mains input to tags "0" and "240" on the top primary side! Chris Williams
__________________
It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 1st Oct 2020 at 9:52 pm. |
2nd Oct 2020, 4:28 pm | #19 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,195
|
Re: DYNATRON HFC77 schematic / transformer
Quite a big beast, certainly rewindable, but cheaper if you can get something close to your spec; no shortage of spave to fit things either
Ed |
2nd Oct 2020, 10:19 pm | #20 | |
Triode
Join Date: Feb 2020
Location: London, UK.
Posts: 21
|
Re: DYNATRON HFC77 schematic / transformer
Quote:
|
|